Synchronizing circuit and clock data recovery circuit including the same
A synchronizing circuit that is capable of generating a reproduced clock signal synchronized with a reference clock signal without causing a false lock and a clock data recovery circuit including the same are provided. To generate a clock signal synchronized with a reference clock signal associated with a data transition point that appears every predetermined period in an input data signal, the following false-lock avoidance processing is performed. That is, precharging of a first line is started when a phase control voltage applied to the first line by a charge pump falls below a lower-limit reference voltage, and the precharging of the first line is continued until the phase control voltage exceeds an upper-limit reference voltage.
1. A synchronizing circuit for generating a reproduced clock signal synchronized with a reference clock signal, the synchronizing circuit comprising:
a charge pump for generating a phase control voltage having a voltage value associated with a phase difference between the reference clock signal and the reproduced clock signal and for delivering the phase control voltage to a first line;
a phase control circuit for providing phase control to the reproduced clock signal depending on said voltage value the phase control voltage; and
a false-lock avoidance circuit for starting to precharge the first line when said voltage value of the phase control voltage falls below a lower-limit reference voltage and for continuing the operation of precharging the first line until said voltage value of the phase control voltage exceeds an upper-limit reference voltage.
2. The synchronizing circuit according to claim 1 , wherein the false-lock avoidance circuit comprises:
a first comparator for comparing magnitudes between the phase control voltage and the lower-limit reference voltage and generating a lower-limit-under signal when the phase control voltage is less than the lower-limit reference voltage;
a second comparator for comparing magnitudes between the phase control voltage and the upper-limit reference voltage and generating an upper-limit-over signal when the phase control voltage is greater than the upper-limit reference voltage, and
a precharge transistor for precharging the first line by applying a supply voltage to the first line in response to the lower-limit-under signal and for stopping the precharging by stopping the application of the supply voltage to the first line in response to the upper-limit-over signal.
3. The synchronizing circuit according to claim 1 , further comprising:
a power-ON reset circuit for generating a one-pulse power-ON reset signal in response to power-on; and
a discharge transistor for discharging the first line in response to the power-ON reset signal for a predetermined duration.
4. The synchronizing circuit according to claim 1 , further comprising:
a power-ON reset circuit for generating a one-pulse power-ON reset signal in response to power-on; and
a discharge transistor for discharging the first line in response to the power-ON reset signal for a predetermined duration.
5. A clock data recovery circuit comprising a clock generation part which generates a reference clock signal synchronized with a data transition point that appears every predetermined period in an input data signal and a synchronizing part which generates a reproduced clock signal synchronized with the reference clock signal,
the synchronizing part comprising:
a charge pump for generating a phase control voltage having a voltage value associated with a phase difference between the reference clock signal and the reproduced clock signal and for delivering the phase control voltage to a first line;
a phase control circuit for providing phase control to the reproduced clock signal depending on said voltage value the phase control voltage; and
a false-lock avoidance circuit for starting to precharge the first line when said voltage value the phase control voltage falls below a lower-limit reference voltage and for continuing the operation of precharging the first line until said voltage value of the phase control voltage exceeds an upper-limit reference voltage.
6. The clock data recovery circuit according to claim 5 , wherein the false-lock avoidance circuit comprises:
a first comparator for comparing magnitudes between the phase control voltage and the lower-limit reference voltage and generating a lower-limit-under signal when the phase control voltage is less than the lower-limit reference voltage;
a second comparator for comparing magnitudes between the phase control voltage and the upper-limit reference voltage and generating an upper-limit-over signal when the phase control voltage is greater than the upper-limit reference voltage; and
a precharge transistor for precharging the first line by applying a supply voltage to the first line in response to the lower-limit-under signal and for stopping the precharging by stopping the application of the supply voltage to the first line in response to the upper-limit-over signal.
7. The clock data recovery circuit according to claim 6 , further comprising:
a power-ON reset circuit for generating a one-pulse power-ON reset signal in response to power-on; and
a discharge transistor for discharging the first line in response to the power-ON reset signal for a predetermined duration.
8. The clock data recovery circuit according to claim 5 , further comprising:
a power-ON reset circuit for generating a one-pulse power-ON reset signal in response to power-on; and
a discharge transistor for discharging the first line in response to the power-ON reset signal for a predetermined duration.
9. A clock data recovery circuit comprising clock generation means for generating a reference clock signal synchronized with a data transition point that appears every predetermined period in an input data signal and synchronizing means for generating a reproduced clock signal synchronized with the reference clock signal,
the synchronizing means comprising:
a charge pump for generating a phase control voltage having a voltage value associated with a phase difference between the reference clock signal and the reproduced clock signal and for delivering the phase control voltage to a first line;
a phase control circuit for providing phase control to the reproduced clock signal depending on said voltage value of the phase control voltage; and
a false-lock avoidance circuit for starting to precharge the first line when said voltage value of the phase control voltage falls below a lower-limit reference voltage and for continuing the operation of precharging the first line until said voltage value of the phase control voltage exceeds an upper-limit reference voltage.
10. The clock data recovery circuit according to claim 9 , wherein the false-lock avoidance circuit comprises:
a first comparator for comparing magnitudes between the phase control voltage and the lower-limit reference voltage and generating a lower-limit-under signal when the phase control voltage is less than the lower-limit reference voltage;
a second comparator for comparing magnitudes between the phase control voltage and the upper-limit reference voltage and generating an upper-limit-over signal when the phase control voltage is greater than the upper-limit reference voltage; and
a precharge transistor for precharging the first line by applying a supply voltage to the first line in response to the lower-limit-under signal and for stopping the precharging by stopping the application of the supply voltage to the first line in response to the upper-limit-over signal.
11. The clock data recovery circuit according to claim 10 , further comprising:
a power-ON reset circuit for generating a one-pulse power-ON reset signal in response to power-on; and
a discharge transistor for discharging the first line in response to the power-ON reset signal for a predetermined duration.
12. The clock data recovery circuit according to claim 9 , further comprising:
a power-ON reset circuit for generating a one-pulse power-ON reset signal in response to power-on; and
a discharge transistor for discharging the first line in response to the power-ON reset signal for a predetermined duration.